1. Field of the Invention
The present invention relates to a semiconductor laser module which is capable of being employed as a pumping light source of an optical amplifier, and an optical amplifier which is capable of being employed in optical communication.
2. Description of the Related Art
In existing optical fiber communication systems, there have been frequently employed rare earth doped fiber amplifiers representatively including an erbium doped optical fiber amplifier to which erbium (Er) has been added (hereinafter referred to as xe2x80x9cEDFAxe2x80x9d). In recent years, a Raman amplifier using Raman amplification action has also been employed.
As a pumping light source used in an optical amplifier, there has been employed a semiconductor laser module of a high output which stabilizes the wavelength by a fiber grating (FBG).
One of the semiconductor laser modules with the FBG is shown in FIG. 5. A laser beam emitted from a semiconductor laser device A is converted into a collimated light beam through a first lens B, and the collimated light beam is condensed onto an input end face of an optical fiber D through a second lens C, to thereby optically couple the semiconductor laser device A with the optical fiber D. The optical fiber D is formed with a fiber grating E that reflects only a light beam having a predetermined wavelength. In the semiconductor laser module shown in FIG. 5, a Peltier device P for temperature control is disposed within a package F, a base K is disposed on the Peltier device P, and a photodiode PD for monitoring, a thermister S and the semiconductor laser device A are mounted on the base K.
As shown in FIG. 6, the FBG of the semiconductor laser module shown in FIG. 5 has, for example, a reflectivity spectrum whose peak reflectivity is about 4% and whose full width half maximum (FWHM) is 2 nm, and feeds back only a part of the laser beam coupled with the optical fiber D to the semiconductor laser device A. Because a loss of the external resonator made up of the semiconductor laser device A and the FBG becomes smaller at only the center wavelength of the FBG, even in the case where a driving current or an ambient temperature of the semiconductor laser device A changes, the oscillation wavelength of the semiconductor laser device A is fixed at the above center wave.
The semiconductor laser module with the FBG is shown in FIG. 7. This semiconductor laser module is so designed as to provide the FBG in a ferrule F into which the optical fiber D is fixedly inserted. In FIG. 7, a protective tube I disposed outside the optical fiber D and a protective boot H disposed outside the protective tube I are also shown.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a semiconductor laser module having a ferrule at a light input side leading end of an optical fiber that receives a light outputted from a semiconductor laser device and transmits the light, wherein an FBG is disposed, outside the ferrule, on the optical fiber inside a protective tube, and a cavity is defined between the FBG and the semiconductor laser device.
According to a second aspect of the present invention, there is provided a semiconductor laser module having a ferrule at a light input side leading end of an optical fiber that receives a light outputted from a semiconductor laser device and transmits the light, wherein an FBG is disposed, outside the ferrule, on the optical fiber inside a protective tube that is disposed inside a protective boot, and a cavity is defined between the FBG and the semiconductor laser device.
According to a third aspect of the present invention, in the semiconductor laser module according to the first or second aspect of the present invention, the FBG is formed inside the protective tube and on the optical fiber at a portion where no adhesive exists.
An optical amplifier according to the present invention uses the semiconductor laser module as defined in any one of the above first to third aspects of the present invention as a pumping light source.